A quantitative study of feeding by the hydroid Tubularia larynx Ellis and Solander, 1786
J.M. Gili, R.G. Hughes, V. Alvà

The natural diet and feeding rate of the benthic hydrozoan Tubularia larynx Ellis & Solander, 1786, were studied by analyzing the enteron contents of fifty hydranths collected approximately every 6h (April 1991) and 4h (September 1993) over two 24h periods. Crustacean eggs, nauplii and copepodids formed a greater proportion of the diet than of the plankton. Copepods and cladocerans formed a smaller proportion of the diet than of the plankton even though they comprised 40% of the identifiable food items. The mean number of prey items per hydranth was closely related to the density of zooplankton, which increased approximately 10 fold at night when more than 90% of the diel prey biomass was captured. The mean number and mean size of prey were positively correlated with hydranth size (width). However, there was an inverse relationship between prey biomass and hydranth biomass, which included some pedicel, since larger hydranths have longer hydrocauli beneath them. The percentage of hydranths containing prey varied between 48 and 100%. The prey frequency distribution differed from the Poisson distribution, with more hydranths having fewer and more prey items than predicted. These data may indicate an innate rhythm of feeding-digestion-egestion. The maximum time taken for items to be digested was estimated to be 5h. It was calculated that each T. larynx hydranth consumed a mean of 36 prey items day-1 (in September 1993). The data from this and other studies indicate that the contribution of hydroids to the transfer of energy from the plankton to the benthos may be much higher than suggested by hydroid biomass values alone.

Keywords: trophic ecology, feeding behaviour, Tubularia larynx, prey capture, prey size, digestion time.
Contents of this volume Sci. Mar. 60(1) : 43-54 Back PDF
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